Polyester-grafted starch-polymer alloy

Abstract

A polyester-grafted starch-polymer alloy is capable of imparting practical flexibility and toughness to moldings with no or only a little plasticizer. The polyester-grafted starch-polymer alloy comprises a blend of a polyester-grafted starch (a starch which has polyester graft chains on the starch molecule, with the terminal hydroxyl groups of the polyester graft chains and the hydroxyl groups connected directly to the starch entirely or partly blocked with the ester group) and an independent polyester (a polyester which is constructed of the same unit as said polyester graft chain, with its terminal hydroxyl groups entirely or partly blocked with the ester group) which are uniformly mixed together. A method of preparing the alloy and thermoplastic resin compositions containing the alloy also are disclosed.

We claim: 
     
       1. A polyester-grafted starch-polymer alloy comprising a blend of a polyester-grafted starch having the formula: ##STR26## and, an independent polyester having the formula:   R.sub.5 -. .CO-(R.sub.4)-O.!..sub.n -R.sub.3               II     where, starch is the residue of starch molecule; R 1  is a member selected from the group consisting of alkyl groups, alkenyl groups, and aryl groups having 1 to 17 carbon atoms; R 2  is a member selected from the group consisting of hydrogen and an acyl group having 2 to 18 carbon atoms, R 3  is a member selected from the group consisting of hydrogen and an acyl group having 2 to 18 carbon atoms, but the R 3  in Formula I and the R 3  in Formula II are not both hydrogen, R 4  is a saturated hydrocarbon group represented by the formula:     C.sub.m H.sub.2m in which m is 1 to 11;     R 5  is a member selected from the class consisting of an alkoxyl group having 1 to 10 carbon atoms, a polyalkoxyl group having 1 to 200 carbon atoms and an hydroxyl group and n is less than 1 to 4000.   
     
     
       2. A polyester-grafted starch-polymer alloy of claim 1, wherein the independent polyester accounts for 5 to 70 wt % therein. 
     
     
       3. A polyester-grafted starch-polymer alloy of claim 1, wherein 15 to 100% of the hydroxyl groups therein are blocked by esterification, the degree of molecular substitution by polyester grafting is 0.1 to 20, and the molecular weight of the polyester graft chain and the independent polyester is about 500 to about 200,000. 
     
     
       4. A polyester-grafted starch-polymer alloy of claim 2, wherein 15 to 100% of the hydroxyl groups therein are blocked by esterification, the degree of molecular substitution by polyester grafting is 0.1 to 20, and the molecular weight of the polyester graft chain and the independent polyester is about 500 to about 200,000.